In countries like Scotland where deer populations are culled, eating wild venison can be a low-carbon option.

My last meat feast was seven years ago. My parents ­were visiting me in London from Costa Rica and we spent the evening going through the brief but rich menu of a small steak restaurant. For them, it was their final meal before returning home; for me, a farewell to my most carnivorous days.

In the years since I've kept a diet of mostly vegetarian dishes, bits of seafood and the occasional exception. As this diet emerged from my work covering climate change, I pick and choose with that in mind: if an animal product is low carbon, like mussels, it will be on my plate regularly. Meat – a high-carbon food – features on my plate for special meals, like my mum's pork leg for Christmas, or on the rare occasion I really crave something like the Costa Rican pork belly-based specialty chifrijo.

Each person has their own approach to climate-friendly food; mine is to reduce food-related emissions, not to have a perfect vegetarian scorecard.

Since I moved to Scotland a few years ago, a new wrinkle has appeared: venison – the meat from deer. Deer populations are out of hand here: the Scottish Government estimates that the overall population could be around one million, up from half a million in 1990. Deer are thriving, partly because humans eradicated their predators, such as wolves and lynx centuries ago.

In response, deer populations are culled every year to keep numbers in check. In my pragmatic climate diet, venison felt like fair game as long as it came from wild deer.

But, was it? This question was on my mind when I was dining at a cosy pub in Mallaig in the Scottish Highlands and spotted venison steak on the menu. Could wild deer really feature in a climate-conscious diet?

"I think the answer here is clearly yes," says Matthew Moran, a professor of biology at Hendrix College in Arkansas, US. Moran co-authored a study in 2020 on the potential carbon savings of wild game harvests in the US.

When Moran's team added up all the animals hunted in US, it was the equivalent of over 3% of all meat consumption nationally. They then asked themselves by how much the country could reduce its meat-related emissions if those hunters swapped shop-bought beef or chicken for their prey (90% of them deer and their relatives).

Their conclusion? The emissions' reduction was equivalent to removing 400,000 cars from the road each year.

"The main reason being is that if you harvest deer from the wild as a food source, there is little or no habitat destruction," Moran explains, "unlike what is involved in raising meat on farms".

Moran's argument rings true, but the answer gets messier the deeper you look. Venison can be a low-carbon option if the deer are not farmed and truly wild. As a meal, wild venison can have a small carbon footprint, as long as hunters don't travel a long way to cull the deer.

Venison can form part of climate-friendly diets on a local level, but the issue grows complicated when considered on a global scale.

"The problem is scale," says Hannah Ritchie, deputy editor and lead researcher at Our World in Data, an organisation that makes scientific data accessible and understandable, and a global development researcher at the University of Oxford in the UK.

"Yes, it might be a reasonable – and low-carbon – choice for a small percentage of the UK population to eat wild venison, but the numbers just don't work for any critical mass of people," she says.

To explore this question, I started with a simpler one: how can one know if something you're eating contributes to climate change?

Beef is a good example of a high-carbon food. The emissions related to all beef cattle are around 5% of global emissions.

When forests or grasslands are cleared to make way for grazing fields and for crops that become animal feed, they release carbon dioxide to the atmosphere. When cows digest food, they naturally produce masses of methane, a potent warming gas. And then there's the fuel used to transport cattle to fields and slaughterhouses, the energy used by retail and storage facilities and every other material involved in the process.

Take all the greenhouse gas emissions associated with beef and divide them by how many burgers you can produce, and you have your carbon footprint per burger.

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